A liquid crystal display apparatus using a conventional liquid crystal display device is described, for example, in Japan Patent Laid-Open No. 178625/1992 and 338721/1992.
FIG. 7 is a cross section showing an example of the structure of a conventional liquid crystal display device. In the liquid crystal display device, the voltage from an active matrix element 18 is applied to a pixel electrode 32. To separate the pixel electrodes 32 and the liquid crystal layer 9, there are provided a dielectric layer 33 and a dielectric mirror 34 between the pixel electrodes 32 and the liquid crystal layer 9. The dielectric mirror 34 is formed of multiple dielectric films. Separating the pixel electrodes 32 and the liquid crystal layer 9 in this way alleviates limitations on the material that can be used for the pixel electrodes 32.
Generally, when the pixel electrodes of the liquid crystal display device are made of a metal to form a reflection surface, there is a problem that the metal surface is prone to corrode at an interface where it is in direct contact with the liquid crystal, degrading the reflectivity of the pixel electrodes. The corrosion also causes deterioration of the liquid crystal, leading to variations in in-plane brightness and color.
To eliminate these problems, it has been suggested to use the dielectric mirror 34 as a reflection surface, as in the conventional technique mentioned above, instead of using metallic pixel electrodes as a reflection surface, and to separate spatially the pixel electrodes 32 and the liquid crystal layer 9. The dielectric mirror 34 is formed as a multilayer film comprising thin films of materials with different refractive indices, such as titanium dioxide and silicon dioxide, stacked alternately one upon the other. As the number of such multilayer films is increased, the reflectivity of the dielectric mirror 34 increases. The increase in the number of multilayer films, however, results in a reduction in an electric capacity.
Light that has leaked through the dielectric mirror 34 is absorbed by a dielectric layer 33, formed flat layer between the dielectric mirror 34 and the pixel electrodes 32, which layer has high visual light absorptivity.
In the conventional technique, as described above, because the dielectric mirror 34 is disposed between the liquid crystal layer 9 and the dielectric layer 33, which is formed over the pixel electrodes 32, the voltage applied between the pixel electrodes 32 and the opposing transparent electrodes 10 through the liquid crystal layer 9 is also shared by the dielectric mirror 34. This reduces the effective voltage applied to the liquid crystal layer 9, making it difficult to drive the liquid crystal display device.
Further, when light leaking through gaps between the pixel electrodes 32 is incident on the circuit of the active matrix element 18, a charge flows out of a storage capacitor therein, causing a photo-activated current leakage. The reflection by the dielectric mirror 34 that prevents this photo-activated current leakage and the undesirable reduction in the effective application voltage to the liquid crystal layer 9 are in a trade-off relationship.
The above conventional technique, however, did not consider this trade-off relationship. In addition, the process of fabricating the dielectric multilayer film is complex, increasing the cost of the liquid crystal display device. Although a protective film is needed to effect spatial separation between the reflective pixel electrodes and the liquid crystal layer, the reduction in the reflectivity of the reflective pixel electrodes caused by this protective film must be avoided.